The potential power for the world in ocean tides and the difficulties that lie in attempting to achieve useful power from that potential are briefly noted in Colliers Encyclopedia (Macmillan, 1980). On page 349 of that reference, it is stated:
Harnessing the energies of ocean tides has long exercised a fascination for the minds of men, and many schemes have been devised and tried in an effort to achieve this goal. But while it is theoretically possible that tidal power could supply upwards of one half of today's world electric power needs, and more power than stream power sources, practical limitations make it very unlikely that this theoretical potential will ever be realized.
The article goes on to state that the geographical site chosen should have a difference of at least 20 feet between high and low tides.
U.S. Pat. No. 1,333,444 states that "in tidal water power plants there is a period of about two hours when the plant cannot work effectively, this being substantially the change of tide". To overcome the problem that patent advocates using three tidal plants along a coast, each about 15 to 20 miles from the adjacent one in a generally north-south line in order to take advantage of the fact that "the time of tidal changes varies considerably with comparatively slight changes in latitude . . . ". Obviously, such a series of plants requires three costly separate installations.
U.S. Pat. Nos. 821,480 and 839,860 describe tide motors which have an upper and lower basin, the one in the former patent with a floating turbine and the one in the latter patent with stationary turbines which drive a dynamo to provide electric power.
U.S. Pat. No. 1,393,472 describes a tide motor comprising a floating barge having the motor mounted thereon, the motor having power-transmitting cogs which engage vertical rack bars anchored to the ocean floor. The rising or descending float causes the power transmitting cogs to be driven by engagement with the rack bars.
Still another tidal motor is described in U.S. Pat. No. 582,651. The tidal motor is mounted on a float with hollow flood and ebb tide sluice gates that may be floated or sunk as required by the tide so as to allow water to turn the turbine.
U.S. Pat. No. 545,241 shows the use of a stationary turbine and the use of a dammed bay which is divided into three lagoons. Valves channel water to and from the sea as required into the turbine so as to produce power.